Multicomponent fiber

ABSTRACT

A fiber containing a longitudinal core (I) of a polymer and a chemically different surrounding sheath (II), wherein said sheath (II) is based on a polyamide containing a sterically hindered piperidine derivative (III) attached to the polymer chain by chemical bonding.

[0001] The present invention relates to a fiber containing alongitudinal core (I) of a polymer and a chemically differentsurrounding sheath (II), wherein said sheath (II) is based on apolyamide containing a sterically hindered piperidine derivative (III)attached to the polymer chain by chemical bonding.

[0002] The present invention further relates to the use of such a fiberfor producing yarn, fabric and carpet.

[0003] The use of polymers, especially polyamides, for producing fiberand yarn is generally known, for example from: Ullmann's Encyclopedia ofIndustrial Chemistry, 5^(th) Ed., Vol. A10, VCH Verlagsgesellschaft mbH,Weinheim, Germany, 1987, pages 567-579.

[0004] Yarn is produced in a conventional manner by melting thepolyamide, spinning the polyamide into a fiber, drawing and texturingthis fiber and optionally aftertreating the fiber. This is customarilyfollowed by cabling and heat setting of the yarn.

[0005] According to Dictionary of Fiber & Textile Technology, HoechstCelanese Corporation, Charlotte, N.C. 28232, USA, 1990, p. 159,texturing, which also comprehends crimping, serves to increase yarncover.

[0006] When carpet is produced from such yarn, a high crimp is desirablebecause high yarn cover means that less yarn is needed to cover acarpet.

[0007] It is an object of the present invention to provide a fiber fromwhich yarn having improved crimp can be produced.

[0008] We have found that this object is achieved by the fiber definedat the beginning and the use of this fiber for producing yarn, fabricand carpet.

[0009] According to the invention, the fiber contains a longitudinalcore (I) of a polymer.

[0010] Useful polymers advantageously include polymers that are meltableand spinnable from the melt, such as polyamides, polyesters,polyolefins, preferably polyamides, polyolefins, especially polyamides.

[0011] Polyamides are herein to be understood as being homopolymers,copolymers, blends and grafts of synthetic long-chain polyamides havingrecurring amide groups in the polymer main chain as an essentialconstituent. Examples of such polyamides are nylon-6 (polycaprolactam),nylon-6,6 (polyhexamethyleneadipamide), nylon-4,6(polytetramethyleneadipamide), nylon-6,10 (polyhexamethylenesebacamide),nylon-7 (polyenantholactam), nylon-11 (polyundecanolactam), nylon-12(polydodecanolactam). As well as polyamides known by the generic name ofnylon, polyamides further include the aramids (aromatic polyamides),such as poly-meta-phenyleneisophthalamide (NOMEX® fiber, U.S. Pat. No.3,287,324) or poly-para-phenyleneterephthalamide (KEVLAR® fiber, U.S.Pat. No. 3,671,542).

[0012] Polyamides can in principle be prepared by two methods.

[0013] In a polymerization from dicarboxylic acids and diamines and alsoin a polymerization from amino acids or their derivatives, such asaminocarbonitriles, aminocarboxamides, aminocarboxylate esters oraminocarboxylate salts, the amino and carboxyl end groups of thestarting monomers or starting oligomers react with one another to forman amide group and water. The water can subsequently be removed from thepolymer. In a polymerization from carboxamides, the amino and amide endgroups of the starting monomers or starting oligomers react with oneanother to form an amide group and ammonia. The ammonia can subsequentlybe removed from the polymer. This polymerization reaction is customarilyknown as a polycondensation.

[0014] A polymerization from lactams as starting monomers or startingoligomers is customarily known as a polyaddition.

[0015] Such polyamides are obtainable by conventional processes,described for example in DE-A-14 95 198, DE-A-25 58 480, EP-A-129 196 orin: Polymerization Processes, Interscience, New York, 1977, pages424-467, especially pages 444-446, from monomers selected from the groupconsisting of lactams, omega-aminocarboxylic acids,omega-aminocarbonitriles, omega-aminocarboxamides,omega-aminocarboxylate salts, omega-aminocarboxylate esters, equimolarmixtures of diamines and dicarboxylic acids, dicarboxylic acid/diaminesalts, dinitriles and diamines or mixtures thereof.

[0016] Useful monomers include

[0017] monomers or oligomers of a C₂ to C₂₀, preferably C₂ to C₁₈,arylaliphatic or, preferably, aliphatic lactam such as enantholactam,undecanolactam, dodecanolactam or caprolactam,

[0018] monomers or oligomers of C₂ to C₂₀, preferably C₃ to C₁₈,aminocarboxylic acids such as 6-aminohexanoic acid or 11-aminoundecanoicacid, and dimers, trimers, tetramers, pentamers or hexamers thereof, andsalts thereof such as alkali metal salts, for example lithium, sodium orpotassium salts,

[0019] C₂ to C₂₀, preferably C₃ to C₁₈, aminocarboxylic acid nitrilessuch as 6-aminocapronitrile or 11-aminoundecanoic acid nitrile,

[0020] monomers or oligomers of C₂ to C₂₀ amino acid amides such as6-aminohexanamide or 11-aminoundecanamide, and dimers, trimers,tetramers, pentamers or hexamers thereof,

[0021] esters, preferably C₁-C₄ alkyl esters, such as methyl, ethyl,n-propyl, i-propyl, n-butyl, i-butyl or s-butyl esters, of C₂ to C₂₀,preferably C₃ to C₁₈, aminocarboxylic acids, such as 6-aminohexanoicacid esters, for example methyl 6-aminohexanoate, or 11-aminoundecanoicacid esters, for example methyl 11-aminoundecanoate,

[0022] monomers or oligomers of a C₂ to C₂₀, preferably C₂ to C₁₂,alkyldiamine, such as tetramethylenediamine or, preferably,hexamethylenediamine, with a C₂ to C₂₀, preferably C₂ to C₁₄, aliphaticdicarboxylic acid or mono- or dinitriles thereof, such as sebacic acid,dodecanedioic acid, adipic acid, sebacic acid dinitrile, decanoic aciddinitrile or adiponitrile, and dimers, trimers, tetramers, pentamers orhexamers thereof,

[0023] monomers or oligomers of a C₂ to C₂₀, preferably C₂ to C₁₂,alkyldiamine, such as tetramethylenediamine or, preferably,hexamethylenediamine, with a C₈ to C₂₀, preferably C₈ to C₁₂, aromaticdicarboxylic acid or derivatives thereof, for example chlorides, such asnaphthalene-2,6-dicarboxylic acid, preferably isophthalic acid orterephthalic acid, and dimers, trimers, tetramers, pentamers or hexamersthereof,

[0024] monomers or oligomers of a C₂ to C₂₀, preferably C₂ to C₁₂,alkyldiamine, such as tetramethylenediamine or, preferably,hexamethylenediamine, with a C₉ to C₂₀, preferably C₉ to C₁₈,arylaliphatic dicarboxylic acid or derivatives thereof, for examplechlorides, such as o-, m- or p-phenylenediacetic acid, and dimers,trimers, tetramers, pentamers or hexamers thereof,

[0025] monomers or oligomers of a C₆ to C₂₀, preferably C₆ to C₁₀,aromatic diamine, such as m- or p-phenylenediamine, with a C₂ to C₂₀,preferably C₂ to C₁₄, aliphatic dicarboxylic acid or mono- or dinitrilesthereof, such as sebacic acid, dodecanedioic acid, adipic acid, sebacicacid dinitrile, decanoic acid dinitrile or adiponitrile, and dimers,trimers, tetramers, pentamers or hexamers thereof,

[0026] monomers or oligomers of a C₆ to C₂₀, preferably C₆ to C₁₀,aromatic diamine, such as m- or p-phenylenediamine, with a C₈ to C₂₀,preferably C₈ to C₁₂, aromatic dicarboxylic acid or derivatives thereof,for example chlorides, such as naphthalene-2,6-dicarboxylic acid,preferably isophthalic acid or terephthalic acid, and dimers, trimers,tetramers, pentamers or hexamers thereof,

[0027] monomers or oligomers of a C₆ to C₂₀, preferably C₆ to C₁₀,aromatic diamine, such as m- or p-phenylenediamine, with a C₉ to C₂₀,preferably C₉ to C₁₈, arylaliphatic dicarboxylic acid or derivativesthereof, for example chlorides, such as o-, m- or p-phenylenediaceticacid, and dimers, trimers, tetramers, pentamers or hexamers thereof,

[0028] monomers or oligomers of a C₇ to C₂₀, preferably C₈ to C₁₈,arylaliphatic diamine, such as m- or p-xylylenediamine, with a C₂ toC₂₀, preferably C₂ to C₁₄, aliphatic dicarboxylic acid or mono- ordinitriles thereof, such as sebacic acid, dodecanedioic acid, adipicacid, sebacic acid dinitrile, decanoic acid dinitrile or adiponitrile,and dimers, trimers, tetramers, pentamers or hexamers thereof,

[0029] monomers or oligomers of a C₇ to C₂₀, preferably C₈ to C₁₈,arylaliphatic diamine, such as m- or p-xylylenediamine, with a C₆ toC₂₀, preferably C₆ to C₁₀, aromatic dicarboxylic acid or derivativesthereof, for example chlorides, such as naphthalene-2,6-dicarboxylicacid, preferably isophthalic acid or terephthalic acid, and dimers,trimers, tetramers, pentamers or hexamers thereof,

[0030] monomers or oligomers of a C₇ to C₂₀, preferably C₈ to C₁₈,arylaliphatic diamine, such as m- or p-xylylenediamine, with a C₉ toC₂₀, preferably C₉ to C₁₈, arylaliphatic dicarboxylic acid orderivatives thereof, for example chlorides, such as o-, m- orp-phenylenediacetic acid, and dimers, trimers, tetramers, pentamers orhexamers thereof,

[0031] and homopolymers, copolymers, mixtures and grafts of suchstarting monomers or starting oligomers.

[0032] In a preferred embodiment, the lactam used is caprolactam, thediamine used is tetramethylenediamine, hexamethylenediamine or theirmixtures and the dicarboxylic acid used is adipic acid, sebacic acid,dodecanedioic acid, terephthalic acid, isophthalic acid or mixturesthereof. Particular preference is given to the lactam being caprolactam,the diamine being hexamethylenediamine and the dicarboxylic acid beingadipic acid or terephthalic acid or their mixtures.

[0033] Particular preference is given to those starting monomers oroligomers which on polymerization lead to the polyamides nylon-6,nylon-6,6, nylon-4,6, nylon-6,10, nylon-6,12, nylon-7, nylon-11 ornylon-12 or the aramids poly-meta-phenyleneisophthalamide orpoly-para-phenyleneterephthalamide, especially to nylon 6 or nylon 66.

[0034] In a preferred embodiment, the polyamides may be prepared usingone or more chain regulators. Useful chain regulators advantageouslyinclude compounds having one or more, such as two, amino groups reactivein polyamide formation or one or more, such as two, carboxyl groupsreactive in polyamide formation.

[0035] The first case provides fibers wherein said monomers used forpreparing said polyamide of said core (I) have a higher number of aminegroups, or their equivalents, used for forming said polymer chain thancarboxylic acid groups, or their equivalents, used for forming saidpolymer chain.

[0036] The second case provides fibers wherein said monomers used forpreparing said polyamide of said core (I) have a higher number ofcarboxylic acid groups, or their equivalents, used for forming saidpolymer chain than amine groups, or their equivalents, used for formingsaid polymer chain.

[0037] Useful chain regulators advantageously include monocarboxylicacids, such as alkanecarboxylic acids, for example acetic acid,propionic acid, such as benzene- or naphthalene-monocarboxylic acid, forexample benzoic acid, dicarboxylic acids, such asC₄-C₁₀-alkanedicarboxylic acid, for example adipic acid, azelaic acid,sebacic acid, dodecanedioic acid, C₅-C₈-cycloalkanedicarboxylic acids,for example cyclohexane-1,4-dicarboxylic acid, benzene- ornaphthalenedicarboxylic acid, for example terephthalic acid, isophthalicacid, naphthalene-2,6-dicarboxylic acid, C₂ to C₂₀, preferably C₂ toC₁₂, alkylamines, such as cyclohexylamine, C₆ to C₂₀, preferably C₆ toC₁₀, aromatic monoamines, such as aniline, or C₇ to C₂₀, preferably C₈to C₁₈, arylaliphatic monoamines, such as benzylamine, diamines, such asC₄-C₁₀-alkanediamines, for example hexamethylenediamine.

[0038] A chain regulator may advantageously be used in amounts of notless than 0.01 mol %, preferably not less than 0.05 mol %, especiallynot less than 0.2 mol %, based on 1 mol of acid amide groups of thepolyamide.

[0039] A chain regulator may advantageously be used in amounts of notmore than 1.0 mol %, preferably not more than 0.6 mol %, especially notmore than 0.5 mol %, based on 1 mol of acid amide groups of thepolyamide.

[0040] In another preferred embodiment, the polymerization orpolycondensation in the process of the invention is carried out in thepresence of at least one pigment. Preferred pigments are titaniumdioxide, preferably titanium dioxide in the anatase modification, orcoloring compounds of inorganic or organic nature. The pigments arepreferably added in an amount of from 0 to 5 parts by weight, especiallyfrom 0.02 to 2 parts by weight, based on 100 parts by weight ofpolyamide. The pigments may be added to the reactor together with thestarting materials or separately therefrom.

[0041] Polyolefins for the purposes of the present invention arehomopolymers, copolymers, blends and grafts of synthetic long-chainpolyolefins obtainable by polymerization of olefinically unsaturatedcompounds, such as ethylene, propylene, styrene, acrylic acid and estersthereof, methacrylic acid and esters thereof, preferably propylene.

[0042] Such polyolefins may be prepared in a conventional manner.

[0043] According to the invention, the core (I) of the fiber issurrounded by a sheath (II), wherein said sheath (II) is based on apolyamide containing a sterically hindered piperidine derivative (III)attached to the polymer chain by chemical bonding.

[0044] Polyamides are herein to be understood as being homopolymers,copolymers, blends and grafts of synthetic long-chain polyamides havingrecurring amide groups in the polymer main chain as an essentialconstituent. Examples of such polyamides are nylon-6 (polycaprolactam),nylon-6,6 (polyhexamethyleneadipamide), nylon-4,6(polytetramethyleneadipamide), nylon-6,10 (polyhexamethylenesebacamide),nylon-6,12 (polyhexamethylenedodecanedioic acid amide), nylon-7(polyenantholactam), nylon-11 (polyundecanolactam), nylon-12(polydodecanolactam). As well as polyamides known by the generic name ofnylon, polyamides further include the so-called aramids (aromaticpolyamides), such as poly-meta-phenyleneisophthalamide (NOMEX® fiber,U.S. Pat. No. 3,287,324) or poly-para-phenyleneterephthalamide (KEVLAR®fiber, U.S. Pat. No. 3,671,542).

[0045] Polyamides can in principle be prepared by two methods.

[0046] In a polymerization from dicarboxylic acids and diamines and alsoin a polymerization from amino acids or their derivatives, such asaminocarbonitriles, aminocarboxamides, aminocarboxylate esters oraminocarboxylate salts, the amino and carboxyl end groups of thestarting monomers or starting oligomers react with one another to forman amide group and water. The water can subsequently be removed from thepolymer. In a polymerization from carboxamides, the amino and amide endgroups of the starting monomers or starting oligomers react with oneanother to form an amide group and ammonia. The ammonia can subsequentlybe removed from the polymer. This polymerization reaction is customarilyknown as a polycondensation.

[0047] A polymerization from lactams as starting monomers or startingoligomers is customarily known as a polyaddition.

[0048] Such polyamides are obtainable by conventional processes,described for example in DE-A-14 95 198, DE-A-25 58 480, EP-A-129 196 orin: Polymerization Processes, Interscience, New York, 1977, pages424-467, especially pages 444-446, from monomers selected from the groupconsisting of lactams, omega-aminocarboxylic acids,omega-aminocarbonitriles, omega-aminocarboxamides,omega-aminocarboxylate salts, omega-aminocarboxylate esters, equimolarmixtures of diamines and dicarboxylic acids, dicarboxylic acid/diaminesalts, dinitriles and diamines or mixtures thereof.

[0049] Useful monomers include

[0050] monomers or oligomers of a C₂ to C₂₀, preferably C₂ to C₁₈,arylaliphatic or, preferably, aliphatic lactam such as enantholactam,undecanolactam, dodecanolactam or caprolactam,

[0051] monomers or oligomers of C₂ to C₂₀, preferably C₃ to C₁₈,aminocarboxylic acids such as 6-aminohexanoic acid or 11-aminoundecanoicacid, and dimers, trimers, tetramers, pentamers or hexamers thereof, andsalts thereof such as alkali metal salts, for example lithium, sodium orpotassium salts,

[0052] C₂ to C₂₀, preferably C₃ to C₁₈, aminocarboxylic acid nitrilessuch as 6-aminocapronitrile or 11-aminoundecanoic acid nitrile,

[0053] monomers or oligomers of C₂ to C₂₀ amino acid amides such as6-aminohexanamide or 11-aminoundecanamide, and dimers, trimers,tetramers, pentamers or hexamers thereof,

[0054] esters, preferably C₁-C₄ alkyl esters, such as methyl, ethyl,n-propyl, i-propyl, n-butyl, i-butyl or s-butyl esters, of C₂ to C₂₀,preferably C₃ to C₁₈, aminocarboxylic acids, such as 6-aminohexanoicacid esters, for example methyl 6-aminohexanoate, or 11-aminoundecanoicacid esters, for example methyl 11-aminoundecanoate,

[0055] monomers or oligomers of a C₂ to C₂₀, preferably C₂ to C₁₂,alkyldiamine, such as tetramethylenediamine or, preferably,hexamethylenediamine, with a C₂ to C₂₀, preferably C₂ to C₁₄, aliphaticdicarboxylic acid or mono- or dinitriles thereof, such as sebacic acid,dodecanedioic acid, adipic acid, sebacic acid dinitrile, decanoic aciddinitrile or adiponitrile, and dimers, trimers, tetramers, pentamers orhexamers thereof,

[0056] monomers or oligomers of a C₂ to C₂₀, preferably C₂ to C₁₂,alkyldiamine, such as tetramethylenediamine or, preferably,hexamethylenediamine, with a C₈ to C₂₀, preferably C₈ to C₁₂, aromaticdicarboxylic acid or derivatives thereof, for example chlorides, such asnaphthalene-2,6-dicarboxylic acid, preferably isophthalic acid orterephthalic acid, and dimers, trimers, tetramers, pentamers or hexamersthereof,

[0057] monomers or oligomers of a C₂ to C₂₀, preferably C₂ to C₁₂,alkyldiamine, such as tetramethylenediamine or, preferably,hexamethylenediamine, with a C₉ to C₂₀, preferably C₉ to C₁₈,arylaliphatic dicarboxylic acid or derivatives thereof, for examplechlorides, such as o-, m- or p-phenylenediacetic acid, and dimers,trimers, tetramers, pentamers or hexamers thereof,

[0058] monomers or oligomers of a C₆ to C₂₀, preferably C₆ to C₁₀,aromatic diamine, such as m- or p-phenylenediamine, with a C₂ to C₂₀,preferably C₂ to C₁₄, aliphatic dicarboxylic acid or mono- or dinitrilesthereof, such as sebacic acid, dodecanedioic acid, adipic acid, sebacicacid dinitrile, decanoic acid dinitrile or adiponitrile, and dimers,trimers, tetramers, pentamers or hexamers thereof,

[0059] monomers or oligomers of a C₆ to C₂₀, preferably C₆ to C₁₀,aromatic diamine, such as m- or p-phenylenediamine, with a C₈ to C₂₀,preferably C₈ to C₁₂, aromatic dicarboxylic acid or derivatives thereof,for example chlorides, such as naphthalene-2,6-dicarboxylic acid,preferably isophthalic acid or terephthalic acid, and dimers, trimers,tetramers, pentamers or hexamers thereof,

[0060] monomers or oligomers of a C₆ to C₂₀, preferably C₆ to C₁₀,aromatic diamine, such as m- or p-phenylenediamine, with a C₉ to C₂₀,preferably C₉ to C₁₈, arylaliphatic dicarboxylic acid or derivativesthereof, for example chlorides, such as o-, m- or p-phenylenediaceticacid, and dimers, trimers, tetramers, pentamers or hexamers thereof,

[0061] monomers or oligomers of a C₇ to C₂₀, preferably C₈ to C₁₈,arylaliphatic diamine, such as m- or p-xylylenediamine, with a C₂ toC₂₀, preferably C₂ to C₁₄, aliphatic dicarboxylic acid or mono- ordinitriles thereof, such as sebacic acid, dodecanedioic acid, adipicacid, sebacic acid dinitrile, decanoic acid dinitrile or adiponitrile,and dimers, trimers, tetramers, pentamers or hexamers thereof,

[0062] monomers or oligomers of a C₇ to C₂₀, preferably C₈ to C₁₈,arylaliphatic diamine, such as m- or p-xylylenediamine, with a C₆ toC₂₀, preferably C₆ to C₁₀, aromatic dicarboxylic acid or derivativesthereof, for example chlorides, such as naphthalene-2,6-dicarboxylicacid, preferably isophthalic acid or terephthalic acid, and dimers,trimers, tetramers, pentamers or hexamers thereof,

[0063] monomers or oligomers of a C₇ to C₂₀, preferably C₈ to C₁₈,arylaliphatic diamine, such as m- or p-xylylenediamine, with a C₉ toC₂₀, preferably C₉ to C₁₈, arylaliphatic dicarboxylic acid orderivatives thereof, for example chlorides, such as o-, m- orp-phenylenediacetic acid, and dimers, trimers, tetramers, pentamers orhexamers thereof,

[0064] and homopolymers, copolymers, mixtures and grafts of suchstarting monomers or starting oligomers.

[0065] In a preferred embodiment, the lactam used is caprolactam, thediamine used is tetramethylenediamine, hexamethylenediamine or theirmixtures and the dicarboxylic acid used is adipic acid, sebacic acid,dodecanedioic acid, terephthalic acid, isophthalic acid or mixturesthereof. Particular preference is given to the lactam being caprolactam,the diamine being hexamethylenediamine and the dicarboxylic acid beingadipic acid or terephthalic acid or their mixtures.

[0066] Particular preference is given to those starting monomers oroligomers which on polymerization lead to the polyamides nylon-6,nylon-6,6, nylon-4,6, nylon-6,10, nylon-6,12, nylon-7, nylon-11 ornylon-12 or the aramids poly-meta-phenyleneisophthalamide orpoly-para-phenyleneterephthalamide, especially to nylon 6 or nylon 66.

[0067] In a preferred embodiment, the polyamides may be prepared usingone or more chain regulators. Useful chain regulators advantageouslyinclude compounds having one or more, such as two, amino groups reactivein polyamide formation or one or more, such as two, carboxyl groupsreactive in polyamide formation.

[0068] The first case provides fibers wherein said monomers used forpreparing said polyamide of said core (I) have a higher number of aminegroups, or their equivalents, used for forming said polymer chain thancarboxylic acid groups, or their equivalents, used for forming saidpolymer chain.

[0069] The second case provides fibers wherein said monomers used forpreparing said polyamide of said core (I) have a higher number ofcarboxylic acid groups, or their equivalents, used for forming saidpolymer chain than amine groups, or their equivalents, used for formingsaid polymer chain.

[0070] Useful chain regulators advantageously include monocarboxylicacids, such as alkanecarboxylic acids, for example acetic acid,propionic acid, such as benzene- or naphthalenemonocarboxylic acid, forexample benzoic acid, dicarboxylic acids, such asC₄-C₁₀-alkanedicarboxylic acid, for example adipic acid, azelaic acid,sebacic acid, dodecanedioic acid, C₅-C₈-cycloalkanedicarboxylic acids,for example cyclohexane-1,4-dicarboxylic acid, benzene- ornaphthalenedicarboxylic acid, for example terephthalic acid, isophthalicacid, naphthalene-2,6-dicarboxylic acid, C₂ to C₂₀, preferably C₂ toC₁₂, alkylamines, such as cyclohexylamine, C₆ to C₂₀, preferably C₆ toC₁₀, aromatic monoamines, such as aniline, or C₇ to C₂₀, preferably C₈to C₁₈, arylaliphatic monoamines, such as benzylamine, diamines, such asC₄-C₁₀-alkanediamines, for example hexamethylenediamine.

[0071] Such chain regulators may carry substituents, such as halogens,for example fluorine, chlorine or bromine, sulfonic acid groups or saltsthereof, such as lithium, sodium or potassium salts, or beunsubstituted.

[0072] Preference is given to sulfonated dicarboxylic acids, especiallysulfoisophthalic acid, and also one of its salts, such as alkali metalsalts, for example lithium, sodium or potassium salts, preferablylithium or sodium salt, especially lithium salt.

[0073] A chain regulator may advantageously be used in amounts of notless than 0.01 mol %, preferably not less than 0.05 mol %, especiallynot less than 0.2 mol %, based on 1 mol of acid amide groups of thepolyamide.

[0074] A chain regulator may advantageously be used in amounts of notmore than 1.0 mol %, preferably not more than 0.6 mol %, especially notmore than 0.5 mol %, based on 1 mol of acid amide groups of thepolyamide.

[0075] According to the invention, the sheath (II) contains a polyamidecontaining a sterically hindered piperidine derivative (III) attached tothe polymer chain by chemical bonding.

[0076] Preference as compounds (III) is given to those of the formula

[0077] where

[0078] R¹ is a functional group capable of amide formation with respectto the polymer chain of the polyamide of sheath (II), preferably a group—(NH)R⁵, in which R⁵ is hydrogen or C₁-C₈ alkyl, or a carboxyl group, ora carboxyl derivative, or a group —(CH₂)_(x)(NH)R⁵, in which X is 1 to 6and R⁵ is hydrogen or C₁-C₈ alkyl, or a group —(CH₂)_(y)COOH, in which Yis 1 to 6, or a —(CH₂)_(y)COOH acid derivative, in which Y is 1 to 6,especially a group —NH₂,

[0079] R² is an alkyl group, preferably a C₁-C₄ alkyl group such asmethyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl or s-butyl,especially a methyl group,

[0080] R³ is hydrogen, C₁-C₄ alkyl or O—R⁴, in which R⁴ is hydrogen orC₁-C₇ alkyl, R³ being hydrogen in particular.

[0081] In such compounds, steric hindrance usually prevents the tertiaryamino groups, and especially the secondary amino groups, of thepiperidine ring system from reacting.

[0082] A particularly preferred compound (III) is4-amino-2,2,6,6-tetramethylpiperidine.

[0083] A compound (III) may advantageously be used in amounts of notless than 0.01 mol %, preferably not less than 0.05 mol %, especiallynot less than 0.1 mol %, based on 1 mol of acid amide groups of thepolyamide.

[0084] A compound (II) may advantageously be used in amounts of not morethan 0.8 mol %, preferably not more than 0.6 mol %, especially not morethan 0.4 mol %, based on 1 mol of acid amide groups of the polyamide.

[0085] In another preferred embodiment, the polymerization orpolycondensation in the process of the invention is carried out in thepresence of at least one pigment. Preferred pigments are titaniumdioxide, preferably titanium dioxide in the anatase modification, orcoloring compounds of inorganic or organic nature. The pigments arepreferably added in an amount of from 0 to 5 parts by weight, especiallyfrom 0.02 to 2 parts by weight, based on 100 parts by weight ofpolyamide. The pigments may be added to the reactor together with thestarting materials or separately therefrom.

[0086] Polyamides advantageously useful as sheath (II), which contain asterically hindered piperidine derivative (III) attached to the polymerchain by chemical bonding, are described for example in WO 95/28443, WO97/05189, WO 98/50610, WO 99/46323, WO 99/48949, EP-A-822 275, EP-A-843696 and the two German applications 10030515.6 and 10030512.1.

[0087] According to the invention, core (I) and sheath (II) arechemically different.

[0088] Advantageously, core (I) and sheath (II) contain a differentamount of sterically hindered piperidine derivative (III) attached tothe polymer chain by chemical bonding, this amount being preferably lessin core (I) than in sheath (II), especially this amount being in core(I), reckoned on a molar basis, less than 50% of this amount in sheath(II). In a particularly preferred embodiment, core (I) contains nosterically hindered piperidine derivative (III) attached to the polymerchain by chemical bonding.

[0089] The fibers may be produced in a conventional manner for exampleas in U.S. Pat. No. 3,803,453, U.S. Pat. No. 5,445,884, U.S. Pat. No.5,447,794, U.S. Pat. No. 5,888,651, EP-A-410 415, EP-A-056 667.

[0090] For instance, the polymer for core (I) and the polyamide forsheath (II) may be prepared separately, a melt of each conveyed by aconveying device, such as an extruder, to a spinneret and spun intofiber there, especially by high speed spinning at takeoff speeds of notless than 4000 m/min.

[0091] In advantageously contemplated fibers, the weight ratio of saidsheath (II) to said core (I) is in the range from 5:95 to 80:20,preferably from 5:95 to 50:50.

[0092] The fiber of the invention may be used in a conventional mannerto produce yarn, fabric and carpet, as already described at thebeginning.

EXAMPLES

[0093] The following polyamides were used:

[0094] Polyamide 1: Ultramid ® UV 2603 C (BASF Aktiengesellschaft),Unpigmented

[0095] Polymerized from 1% by weight of lithium sulfoisophthalate, 0.07%by weight of hexamethylenediamine, 0.15% by weight of4-amino-2,2,6,6-tetramethylpiperidine, remainder caprolactam

[0096] Polyamide 2: Ultramid ® UV 2603 C (BASF Aktiengesellschaft),Pigmented

[0097] Polymerized from 1% by weight of lithium sulfoisophthalate, 0.07%by weight of hexamethylenediamine, 0.15% by weight of4-amino-2,2,6,6-tetramethylpiperidine, 0.3% by weight of titaniumdioxide, remainder caprolactam

[0098] Polyamide 3: Ultramid ® BS 700 (BASF Aktiengesellschaft),Unpigmented

[0099] Polymerized from 0.15% by weight of propionic acid, remaindercaprolactam

[0100] Polyamide 4: Ultramid ® BS 700 (BASF Aktiengesellschaft),Pigmented

[0101] Polymerized from 0.15% by weight of propionic acid, 0.3% byweight of Palamid Red color pigment, remainder caprolactam

[0102] The polyamides of table 1 were used to spin 2700 dtex round fiberhaving a weight ratio of 70:30 for core (I) to sheath (II), which wasdraw-textured to obtain the data shown in the Table. TABLE 1 ExampleCore Sheath Crimp [%] Inventive 1 Polyamide 1 Polyamide 4 5.1 Inventive2 Polyamide 3 Polyamide 3 5.1 Comparative 1 Polyamide 4 4.8 Comparative2 Polyamide 2 4.5

[0103] The table shows that the inventive fibers possess better crimpthan prior art fibers consisting exclusively of the material of sheath(II) (comparative example 1) or exclusively of the material of core (I)(comparative example 2).

We claim:
 1. A fiber containing a longitudinal core (I) of a polymer anda chemically different surrounding sheath (II), wherein said sheath (II)is based on a polyamide containing a sterically hindered piperidinederivative (III) attached to the polymer chain by chemical bonding. 2.The fiber of claim 1, wherein the weight ratio of said sheath (II) tosaid core (I) is in the range from 5:95 to 80:20.
 3. The fiber of claim1, wherein the weight ratio of said sheath (II) to said core (I) is inthe range from 5:95 to 50:50.
 4. The fiber of any of claims 1 to 3,wherein said sheath (II) contains from 0.03 to 0.8 mol %, based on 1 molof acid amide group of said polyamide in said sheath (II), of amineradical of the formula (III).
 5. The fiber of any of claims 1 to 4,wherein compound (III) is 4-amino-2,2,6,6-tetramethylpiperidine and itis attached to said polymer chain by an amide bond.
 6. The fiber of anyof claims 1 to 5, wherein said sheath (II) is based on a polyamideobtainable from monomers selected from the group consisting of lactams,omega-aminocarboxylic acids, omega-aminocarbonitriles,omega-aminocarboxamides, omega-aminocarboxylate salts,omega-aminocarboxylate esters, equimolar mixtures of diamines anddicarboxylic acids, dicarboxylic acid/diamine salts, dinitriles anddiamines or mixtures thereof.
 7. The fiber of any of claims 1 to 6,wherein said core (I) is based on a polyamide.
 8. The fiber of any ofclaims 1 to 7, wherein said core (I) is based on a polyamide obtainablefrom monomers selected from the group consisting of lactams,omega-aminocarboxylic acids, omega-aminocarbonitriles,omega-aminocarboxamides, omega-aminocarboxylate salts,omega-aminocarboxylate esters, equimolar mixtures of diamines anddicarboxylic acids, dicarboxylic acid/diamine salts, dinitriles anddiamines or mixtures thereof.
 9. The fiber of any of claims 1 to 8,wherein the lactam used is caprolactam.
 10. The fiber of any of claims 1to 9, wherein the diamine used is tetramethylenediamine,hexamethylenediamine or their mixture.
 11. The fiber of any of claims 1to 10, wherein the dicarboxylic acid used is adipic acid, sebacic acid,dodecanedioic acid, terephthalic acid, isophthalic acid or a mixturethereof.
 12. The fiber of any of claims 1 to 11, wherein said sheath(II) contains a sulfonated dicarboxylic acid, or a salt thereof, bondedto the polymer chain.
 13. The fiber of claim 12, wherein said sulfonateddicarboxylic acid is sulfoisophthalic acid.
 14. The fiber of any ofclaims 1 to 13, wherein said monomers used for preparing said polyamideof said sheath (II) have a higher number of amine groups, or theirequivalents, used for forming said polymer chain than carboxylic acidgroups, or their equivalents, used for forming said polymer chain. 15.The fiber of any of claims 1 to 13, wherein said monomers used forpreparing said polyamide of said sheath (II) have a higher number ofcarboxylic acid groups, or their equivalents, used for forming saidpolymer chain than amine groups, or their equivalents, used for formingsaid polymer chain.
 16. The use of fiber as claimed in any of claims 1to 15 for producing yarn, fabric and carpet.